The present invention relates to a valve repair device and more specifically, a valve repair device for gas containing containers such as seamless pressure tubes and cylinders.
Gases such as boron trifluoride are typically shipped as compressed gases in seamless high pressure tubes and cylinders at pressures between 1,500 and 2,000 pounds per square inch gauge (psig) (10,500 and 14,000 kPa). A commonly used seamless pressure tube has a valve for loading the gas into the tube and subsequently releasing the gas from the tube. A commonly used valve has a threaded cylindrical portion which receives a stem and a polymeric valve gasket. A packing nut also is screwed onto the threaded cylindrical portion to compress the polymeric valve gasket. Frequently, these valves crack at the threaded cylindrical portion either in a vertical or a horizontal direction or on the packing nut in a horizontal direction as explained more fully below.
When a compressed gas such as boron trifluoride is released from a seamless pressure tube, the gas temperature decreases due to the pressure drop (Joule-Thomson Effect) and as a result, the polymeric valve gasket contracts and gas may begin to leak through the valve packing. A worker then tightens the valve packing nut to seal the leak. When the temperature then increases, the polymeric valve gasket expands against the threaded cylindrical portion of the valve. This expansion may cause the threaded cylindrical portion of the valve or the packing nut to crack.
Gas then begins to immediately leak from the seamless pressure tube through the cracked valve. The leaking of boron trifluoride is readily apparent because in the presence of water, boron trifluoride fumes and forms clouds of dense white smoke with a sharply acidic odor. Boron trifluoride gas is an acid-like pulmonary irritant which attacks mucous membranes and may result in acute toxic effects. As such, breathing of boron trifluoride gas, or fumes formed by hydration of the gas with atmospheric moisture, must be avoided. The problem of toxic gases leaking through cracked valves on high pressure tubes has plagued the industry for years.
Gases such as chlorine are typically shipped as compressed gases in low pressure cylinders at pressures between 100 and 150 pounds per square inch gauge (psig) (700 and 1,050 kPa). Low pressure cylinders typically hold about 60 pounds of product and are shipped in pallets. The leaking of chlorine is apparent because in the presence of ammonia water, chlorine fumes and forms clouds of dense white smoke. Chlorine gas is toxic as an irritant and by inhalation.
One system which has been successful in containing a leaking gas from a low pressure cylinder is The Chlorine Institute's Emergency A Kit. In this system, two workers roll the tube on end onto a base having three chains connected thereto; the length of each chain exceeds the length of the tube. One of the workers then places a metallic hood over the valve end of the tube with a rubber gasket to seal the gap between the metallic cap and the tube body and then places a yoke having cap screws on the top of the metallic hood. The other worker then hooks each chain onto the yoke and tightens the cap screws. As such, this system contains any gas within the metallic hood and rubber gasket.
The Chlorine Institute's Emergency A Kit was not designed to handle high pressure tubes and high pressure cylinders and therefore, is not useful therewith. If a worker attempted to use such a kit with tubes at pressures greater than about 200 psig (1,400 kPa), the metallic hood would be unable to withstand the pressure and thus, would not contain the leaking gas.
The Chlorine Institute's Emergency A Kit also suffers from the following disadvantages. The Chlorine Institute's Emergency A Kit merely provides for containment of the leaking gas. Also, a typical trailer for transporting and storing gas filled seamless pressure tubes may carry as many as thirty tubes in a stacked arrangement. Because the tubes may spend months or years on a trailer at a customer's location, valve cracks can readily occur. Because The Chlorine Institute's system requires access to the tube body as well as the valve and because only the valve ends of tubes on a trailer are readily accessible to an installer, this system is inapplicable to cracked valves on tubes loaded on a trailer. Also, due to the lengthly installment time involved, The Chlorine Institute recommends that the installers wear protective clothing and a self-contained breathing apparatus. Also, due to the equipment involved, two workers are required to install the system. Additionally, The Chlorine Institute considers the Emergency A Kit as an interim measure and recommends emptying the gas from the tube as soon as possible.
As such, a long-felt need has existed for a repair device for cracked valves on high pressure tubes.